BERLIN, April 26 (Reuters) - The U.S. Marine Corps is on track to declare an initial four CH-53K heavy-lift helicopters, built by Lockheed Martin Corp's Sikorsky unit, ready for combat use as planned in December 2019, senior Marine Corps officials said on Thursday.

Colonel Hank Vanderborght, who manages the CH-53K programme for the U.S. military branch, told reporters at the ILA Berlin Air Show the new aircraft was performing well in testing, and "many, many" routine technical issues that emerged during development had been solved.

He dismissed as "dated" a Pentagon document leaked earlier this week which cited over 1,000 current or projected deficiencies that could delay the December 2019 goal.

"We are on our timeline. Timelines can always change, but right now we’re on target," he said.

The current plan called for the Marines to carry out an operational evaluation after testing ends in December 2019 that will pave the way for a declaration of "initial operational capability".

Marine Corps Assistant Commandant General Glenn Walters said he was confident the Marines would meet their schedule.

The CH-53K, which offers three times the carrying power of its predecessor, made its international debut at the Berlin show on Wednesday after being transported to Germany in a C-17 transport plane.

Germany will choose between the CH-53K and Boeing Co's smaller, twin-rotor CH-47 Chinook to replace its ageing fleet of CH-53G heavy-lift helicopters, an order valued at around 4 billion euros.

The German defence ministry expects to release a formal request for proposals in the second half of 2018, with a contract award due in mid-2020, for deliveries to start in 2023.

Sikorsky President Dan Schultz told reporters in a separate briefing his company was working hard to reduce the expected average procurement cost of $87 million for each of the CH-53K helicopters.

Purchases by Germany, which is considering buying 45 to 60 aircraft, and Israel, which wants to purchase over 20 aircraft, could help drive the cost down further by increasing efficiencies and order quantities, he said. (Reporting by Andrea Shalal; editing by Andrew Roche)